# Enforcing Monotonic Progress in Legal Cross-Examination: Preventing Long-Horizon Stagnation in LLM-Based Inquiry

Source: [Enforcing Monotonic Progress in Legal Cross-Examination: Preventing Long-Horizon Stagnation in LLM-Based Inquiry](<https://www.sota2.com/research/paper/69842469a8b01e76cc8ee968>)

Collection index: [llms.txt](<https://www.sota2.com/research/llms.txt>)

Data updated: 2026-02-06T05:00:04.455Z

Authors: Hsien-Jyh Liao

Published: 2026-02-04T04:44:56.000Z

## Abstract

Large language models (LLMs) exhibit impressive linguistic fluency but struggle to reliably complete long-horizon tasks under explicit procedural constraints. In legal cross-examination, purely proba-bilistic generation often maintains behavioral coherence while failing to ensure procedural advancement. We characterize this failure as procedural stagnation and propose Soft-FSM, a neuro-symbolic architecture that enforces monotonic progress over accumulated Key Information Units (KIUs) via an external deterministic state controller. Experiments on three real-world Taiwanese criminal homicide cases show that baseline methods collapse below 40% completeness, while Soft-FSM consistently achieves over 97% with near-zero redundancy. These results suggest that, in such domains, reliable task completion cannot be guaranteed by emergent LLM behavior alone, and can be reliably enforced through explicit and verifiable external state control.

## Recorded benchmark results

A research result applies to its stated dataset, split, metric and evaluation configuration. Compare like-for-like settings, preserve the metric's unit and direction, and distinguish paper-reported results from independent reproduction. The best result recorded here is not a claim of exhaustive, current global coverage.

- [Long-horizon legal inquiry on Taiwanese criminal case Simple (Case A)](<https://www.sota2.com/research/sota/long-horizon-legal-inquiry-on-taiwanese-criminal-case-simple-case-a.md>): Long-horizon legal inquiry; Taiwanese criminal case Simple (Case A); Completeness: 97.2.

- [Long-horizon legal inquiry on Taiwanese criminal case Complex (Case B)](<https://www.sota2.com/research/sota/long-horizon-legal-inquiry-on-taiwanese-criminal-case-complex-case-b.md>): Long-horizon legal inquiry; Taiwanese criminal case Complex (Case B); Completeness: 97.2.

- [Long-horizon legal inquiry on Taiwanese criminal case Abstract (Case C)](<https://www.sota2.com/research/sota/long-horizon-legal-inquiry-on-taiwanese-criminal-case-abstract-case-c.md>): Long-horizon legal inquiry; Taiwanese criminal case Abstract (Case C); Completeness: 98.6.

## Original sources and implementation

[Original paper](<https://arxiv.org/abs/2602.04206>)

[PDF](<https://arxiv.org/pdf/2602.04206.pdf>)